The secret Cold War telephone exchange under Holborn

High Holborn looks like any other stretch of central London: buses, a Tube entrance, offices above shops. Forty metres below it runs 8,000 square metres of tunnel that spent three decades as a working telephone exchange nobody outside the Post Office was meant to know about, built inside a shelter designed for an air raid that never filled it.

It is one of the stranger footnotes to a network you can explore properly at dailymetro.live/london/explore, because it was never a station at all, just tunnels bored in the same style, for a different war.

Built as a deep-level shelter, never used as one

During the Second World War, London Underground bored a set of deep-level shelters under existing Tube stations, wide enough to be converted into new express tunnels once peace came. That postwar conversion never happened. The Chancery Lane shelter, roughly 40 metres below High Holborn, sat largely unused for its intended purpose: sheltering the public through the Blitz.

1944: taken over by Churchill's Secret Army

By 1944 the tunnels were in the hands of the Inter-Services Research Bureau, the cover name for the Special Operations Executive, the sabotage and resistance-support organisation Winston Churchill called his Secret Army. What exactly ran through the tunnels in this period is thin on public record, which is rather the point of a wartime intelligence outfit, according to Wikipedia and Subterranea Britannica.

It is a different underground wartime site from Down Street, the closed Piccadilly line station a few miles west that briefly sheltered the Railway Executive Committee, but the two sit in the same category: ordinary Tube infrastructure repurposed for a war that needed places nobody would think to look.

1949 to 1956: the GPO moves in, and the Cold War moves in with it

The General Post Office took over the site in 1949 and fitted it out as a protected telephone exchange, hardened against exactly the kind of attack the Cold War was expected to bring. In 1956 it became the UK's landing point for TAT-1, the first transatlantic telephone cable, linking Britain directly to North America down copper laid across the ocean floor, according to CNN and thelondontunnels.com.

At various points the exchange is reported to have carried the direct Moscow-Washington hotline connection, the sort of infrastructure that justifies putting a telephone network 40 metres underground in the first place.

5,000 trunk cables, 200 staff, and the deepest bar in Britain

At its busiest the exchange carried around 5,000 trunk cables and employed roughly 200 people working shifts underground, far enough down that London Transport Museum-style day trips were never on offer. Staff had their own bar, reputed to be the deepest in the United Kingdom at about 60 metres below street level, a small piece of ordinary life bolted onto a facility built for none.

The tunnels are also rumoured, unverified but persistent, to have inspired Q Branch in the James Bond films: a hidden, gadget-filled workshop under an unremarkable London street is not a hard leap to make once you know one existed.

Decommissioned, and now heading for the public

As trunk telephony moved to digital and satellite links, the exchange's usefulness faded and it was largely wound down through the 1980s. The site has since changed hands more than once, and a redevelopment project called The London Tunnels has proposed opening sections of it to visitors, turning a Cold War secret into a ticketed attraction, as reported by Londonist.